This proposal seeks to identify the bacteria present in human periodontal disease at the site of disease initiation and progression. It will further determine the quantity of each organism identified relative to the total number of organisms present, and assess the variability quantitatively at different sites, among individuals, and on repeated samples from the same site. Thus, baselines will be established for the reliability of single samples and the numbers of specific organisms present, related to total number of organisms present. The determinations will be made at the two ends of the spectrum of the most common form of periodontal disease, gingivitis-periodontitis; that is, gingivitis after starting from a healthy baseline, and severe periodontitis. Results from both groups will later be used for comparison to similar investigation in different severities of gingivitis-periodontitis and in other forms of periodontal disease. Results from study of the severe periodontitis group will complement on-going study of such a group relative to their immunologic status and responsiveness, and will aid in intelligent antigen selection for such studies. It is probable that previously undescribed organisms will be identified, and thus can be made available, descriptively and for purposes of comparison to isolates in other laboratories, to other investigators in similar or related studies.